The present invention relates to a method of testing braces designed to restrain objects relative to a fixed structure during an earthquake, for example, to restrain sprinkler pipes in a building.
Design codes and standards (e.g., Uniform Building Code, International Building Code, NFPA-13 (National Fire Protection Association)) estimate the amplitude of the seismic load in sprinkler-pipe braces, but they do not specify the number of cycles for which this load must be resisted by various components of pipe braces.
The sprinkler pipes in a building are typically supported from the roof or the floor above by hanger rods that are designed to transfer the gravity load from the pipes to the supporting structure. In seismic regions, the pipes need to be restrained laterally and longitudinally at discrete locations along their length by seismic braces. In an earthquake, inadequately restrained sprinkler piping can suffer damage by large differential movement within the piping or by impacts with adjacent structural and nonstructural components. In the past, seismic damage to sprinkler pipes has been in the form of broken sprinkler heads, failed couplings and fittings, unseated hanger-rods and broken braces. To perform their function, the seismic braces must resist the dynamic load imposed by the vibrating sprinkler-pipe without breaking or deforming excessively.
Design codes and standards estimate the amplitude of the seismic load, but they do not estimate the number of cycles for which the load is applied.